1. Technical Field
The present invention relates in general to a memory and a manufacturing method thereof. More particularly, this invention relates to a memory of which the word lines and the string select structures are formed by different processing steps, and a manufacturing method thereof.
2. Description of the Related Art
For high-density memory devices, the amount of data per unit area on an integrated circuit is a critical factor. As such, three-dimensional (3D) memory array structures have been developed to achieve greater storage density and lower costs per bit.
In a typical 3D memory array, a plurality of stacks of alternate semiconductor strips and insulating strips are formed, wherein the semiconductor strips are used, for example, as bit lines of the memory. A memory layer is formed on the stacks. Word lines are formed on the memory layer orthogonally to the stacks. At one end of the structure, every other stack is terminated by a stair-step structure, and every other stack is terminated by one of separate source contacts. The stacks terminated by the stair-step structure at said end are terminated by separate source contacts at the other end of the structure, and the stacks terminated by the separate source contacts at said end are terminated by a stair-step structure at the other end. The stacks are coupled to string select structures through portions near the ends terminated by the stair-step structures. In general, the string select structures are patterned at the same step that the word lines are defined.